Qingbo (Spinibarbus sinensis) personalities and their effect on shoaling behavior

Group-level behavior has important fitness consequences for group-living fish, which might be affected by the personalities of group members. However, the role of group personality on group behavior has seldom been systematically investigated. To test the effect of the personalities of group members on shoaling behavior and the underlying mechanisms, we investigated the activity and boldness personality traits in qingbo (Spinibarbus sinensis) and grouped qingbo shoals into high personality score, low personality score, and randomly selected control groups and measured the shoal-level behavior traits. Compared with the reactive shoal (low activity and boldness), the proactive (high activity and boldness) shoal showed high activity and increased synchronization of speed, suggesting that the shoal-level behavior was affected by the personalities of the shoal members. Interestingly, the variables in the control shoal were midway between those in the high- and low-activity shoals, suggesting that the average activity score might be the most important factor for group-level behavior (average-determined mechanism). However, when qingbo were divided into high- and low-boldness shoals, the control shoal variables were similar to those of the low-boldness shoals, suggesting that a minority of low-boldness individuals might have a dominant effect on shoal-level behavior (minority-determined mechanism). Cohesion showed a more complicated pattern than the other variables, which might be because the conformity of personalities among shoal members had a profound effect on cohesion. This finding suggests that large interindividual differences in personality play a profound effect on group-level behavior, and different mechanisms might provide the precondition for shoals to exhibit great shoal-level diversity. These findings might have important ecological relevance for the survival of group-living fish in habitats with food resource and predation intensity fluctuations.